I was lucky enough to be present when I got mine done so I witnessed the whole process.
Dash doesn't need to come out. On my S9, the airbag assembly is dropped down after removal of the glove box, central locking and NATS modules.
Although only the inflator is the suspect part, the entire airbag assembly needs to be replaced. The new inflator is a slightly different size than the old one, so it doesn't fit in the old airbag. The airbag and inflator are supplied separately and need to be pre-assembled by the dealer. The inflator is common for various models. The airbag is obviously not.
The inflator is held in position by 4 special nuts that cannot be reused and are part of the kit. The kit also includes a replacement harness that connects directly to the inflator. The connector on the harness cannot be removed from the inflator without destroying it, once it's clipped in, which is why it's also replaced.
New inflator and airbag serial numbers are recorded against the VIN on a Nissan global website, so they know exactly which parts went into the vehicle.
All in all, it's a fairly simple process. The most difficult part is the pre-assembly because you have to be careful to ensure the inflator is installed correctly (without damaging the new airbag) and the nuts are tightened to the correct torque.
The old inflator that came out of my car looked brand new and had no signs of corrosion however, the car is only 4 years old and is permanently garaged in Melbourne. High temperature and humidity are major contributing factors. My car has been well protected against this all its life.
Nissan has plenty stock of replacement parts. There's no reason why you can't get it done within a reasonable time period. Also, dealers are obliged to give customers a loan car if necessary so you really have no excuse not to get it done.
Car companies and dealers are caught between a rock and a hard place. The ACCC is leaning heavily on manufacturers to get it done in a short space of time, but dealers are having to manage "difficult" customers who don't really see this as a priority. I'm all for de-registration of vehicles that does not comply. The biggest problem is not the dealers or the car companies, but the actual owners of these cars.
You can lead a horse to water, but you can't make him drink. I'd suggest watching the 60 minutes report on Channel 9. It will give you some insight on what can potentially happen if a faulty inflator is triggered.